In a typical process for the production of ethylene glycol, ethylene oxide is hydrolyzed with water at elevated temperature and pressure, the ethylene oxide being typically produced by direct oxidation of ethylene with air or elemental oxygen in the presence of a catalyst, typically a silver-containing catalyst at elevated temperature and pressure.
The glycol stream resulting from the reaction of ethylene oxide with water is passed through evaporator means wherein the glycol is concentrated and the concentrated glycol is passed through fractioning means wherein remaining water is removed and monoethylene glycol, diethylene glycol and triethylene glycol are separated each from the other.
Glycols produced by this process often have ultraviolet light absorption characteristics which render them unsuitable for use in the manufacture of polyester fibers due to impurities which absorb ultraviolet radiation, which impurities can only be removed with difficulty by further processing such as for example, distillation. A typical specification for fiber grade monoethylene glycol requires that the glycol have ultraviolet transmittances of at least 70, 90, 95, and 98 percent at 220, 250, 275, and 350 nanometers respectively.
The nature of these ultraviolet light absorbing impurities and the mechanism by which they are formed is open to conjecture. In for example, U.S. Pat. No. 3,970,711 impurities identified as mesityl oxide and ethylene carbonate are believed to result from the feeding and subsequent hydrolysis of stripper bottoms from the ethylene oxide purification system to the glycol reaction system. It has also been found that hydrolysis of ethylene oxide stripper bottoms form quantities of crotonaldehyde and 2,4-hexadienal. Moreover ultraviolet light absorbing impurities are also believed to be formed directly from the hydrolysis of ethylene oxide with water to produce ethylene glycol.
The aforementioned U.S. Pat. No. 3,970,711 also describes means of reducing the level of impurities in the product glycol by treating the glycol containing stripper bottoms from the ethylene oxide purification system with an adsorbent material e.g. activated carbon, prior to feeding the stripper bottoms to the glycol system. Although this process could be effective in removing impurities contained in the ethylene oxide stripper bottoms, it would not remove any impurities formed directly in the hydrolysis of ethylene oxide with water.